This application relates to a hydrodynamic bearing. In one example, the hydrodynamic bearing may be used as a thrust bearing in, for example, an air cycle machine, a RAM air fan and/or a motor driven compressor.
Hydrodynamic thrust bearings are used between a stationary component, such as a housing, and a disc or thrust runner that can rotate at speeds in excess of 50,000 rpm. The hydrodynamic bearing operates by sustaining an air film that provides lubrication between the stationary component and the thrust runner. Hydrodynamic bearings must perform at low speeds with a sufficient air film. It is also desirable to manufacture the hydrodynamic bearing with as few parts as possible.
In one prior art arrangement, a hydrodynamic bearing includes a main foil with multiple top foils secured to the main foil. A bump foil is arranged under each of the top foils adjacent to the main foil. Spacers are arranged on the opposite side of the main foil from the top and bump foils. This arrangement requires a more complex top foil design that uses a bend or step to arrange the top foil over the bump foil. This step creates several problems. First, since air pressure is a function of rotation speed, higher speeds are required to generate sufficient pressure for desired aerodynamic top foil performance due to the drag created by the step. Second, the step allowed increased leakage between the foils.
What is needed is a more aerodynamic hydrodynamic bearing. Current air bearings are rather complex and require many parts. Thus, it is also desirable to reduce the number of parts and simplify the manufacturing process.